The goal of this project is to develop the use of peptide aptomers that interfere with protein function in vivo. Peptide aptomers are short peptides (fused to a platform molecule, E. coli thioredoxin) that interact specifically with a target protein. Aptomers that disrupt specific protein/ protein interactions can be selected using the yeast two-hybrid system and then expressed in Drosophila in spatially and temporally controlled patterns. Previous results from this group have shown that peptide aptomers can be used to specifically target and inhibit cell cycle regulators in vivo, and using two hybrid approaches they have identified a network of protein interactors, that includes known and potential cell cycle regulators. The proposal has four Specific Aims. 1) To improve the technology for the isolation and subcloning of aptomers. 2) To test the aptomer approach by expressing aptomers that disrupt interactions between Cdk2, Cyclin E and Dacapo in the Drosophila eye. 3) To partially characterize novel proteins from a network of interacting proteins to identify a core group that are likely to regulate the cell cycle in the developing eye. 4) To use peptide aptomers to analyze the function of this core group of proteins.